PM 566 Assignment 1

Chris Hanson

September 24, 2021

In this assignment I am given the task of determining whether daily concentration of PM2.5 has decreased in California in the last 15 years. To do this I am using data provided by the U.S. EPA.

rm(list = ls())

# Load libraries
library(tidyverse)
library(data.table)
library(janitor)
library(leaflet)
library(ggplot2)

Problem 1. Read in the data. Check dimensions, headers, footers, variable names, and variable types. Check for any data issues, particularly in the key variables. Summarize all findings.

# Read in the data using data.table().
pm2004 <- data.table::fread("ad_viz_plotval_data_2004.csv")
pm2004 <- clean_names(pm2004)
pm2019 <- data.table::fread("ad_viz_plotval_data_2019.csv")
pm2019 <- clean_names(pm2019)
# Check dimensions
paste("The 2004 dataset has", dim(pm2004)[1], "observations and", dim(pm2004)[2], "variables.")

## [1] "The 2004 dataset has 19233 observations and 20 variables."

paste("The 2019 dataset has", dim(pm2019)[1], "observations and", dim(pm2019)[2], "variables.")

## [1] "The 2019 dataset has 53086 observations and 20 variables."

# Check headers
head(pm2004)

##          date source  site_id poc daily_mean_pm2_5_concentration    units
## 1: 01/01/2004    AQS 60010007   1                           11.0 ug/m3 LC
## 2: 01/02/2004    AQS 60010007   1                           12.2 ug/m3 LC
## 3: 01/03/2004    AQS 60010007   1                           16.5 ug/m3 LC
## 4: 01/04/2004    AQS 60010007   1                           19.5 ug/m3 LC
## 5: 01/05/2004    AQS 60010007   1                           11.5 ug/m3 LC
## 6: 01/06/2004    AQS 60010007   1                           32.5 ug/m3 LC
##    daily_aqi_value site_name daily_obs_count percent_complete
## 1:              46 Livermore               1              100
## 2:              51 Livermore               1              100
## 3:              60 Livermore               1              100
## 4:              67 Livermore               1              100
## 5:              48 Livermore               1              100
## 6:              94 Livermore               1              100
##    aqs_parameter_code                     aqs_parameter_desc cbsa_code
## 1:              88502 Acceptable PM2.5 AQI & Speciation Mass     41860
## 2:              88502 Acceptable PM2.5 AQI & Speciation Mass     41860
## 3:              88502 Acceptable PM2.5 AQI & Speciation Mass     41860
## 4:              88502 Acceptable PM2.5 AQI & Speciation Mass     41860
## 5:              88502 Acceptable PM2.5 AQI & Speciation Mass     41860
## 6:              88502 Acceptable PM2.5 AQI & Speciation Mass     41860
##                            cbsa_name state_code      state county_code  county
## 1: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 2: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 3: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 4: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 5: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 6: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
##    site_latitude site_longitude
## 1:      37.68753      -121.7842
## 2:      37.68753      -121.7842
## 3:      37.68753      -121.7842
## 4:      37.68753      -121.7842
## 5:      37.68753      -121.7842
## 6:      37.68753      -121.7842

head(pm2019)

##          date source  site_id poc daily_mean_pm2_5_concentration    units
## 1: 01/01/2019    AQS 60010007   3                            5.7 ug/m3 LC
## 2: 01/02/2019    AQS 60010007   3                           11.9 ug/m3 LC
## 3: 01/03/2019    AQS 60010007   3                           20.1 ug/m3 LC
## 4: 01/04/2019    AQS 60010007   3                           28.8 ug/m3 LC
## 5: 01/05/2019    AQS 60010007   3                           11.2 ug/m3 LC
## 6: 01/06/2019    AQS 60010007   3                            2.7 ug/m3 LC
##    daily_aqi_value site_name daily_obs_count percent_complete
## 1:              24 Livermore               1              100
## 2:              50 Livermore               1              100
## 3:              68 Livermore               1              100
## 4:              86 Livermore               1              100
## 5:              47 Livermore               1              100
## 6:              11 Livermore               1              100
##    aqs_parameter_code       aqs_parameter_desc cbsa_code
## 1:              88101 PM2.5 - Local Conditions     41860
## 2:              88101 PM2.5 - Local Conditions     41860
## 3:              88101 PM2.5 - Local Conditions     41860
## 4:              88101 PM2.5 - Local Conditions     41860
## 5:              88101 PM2.5 - Local Conditions     41860
## 6:              88101 PM2.5 - Local Conditions     41860
##                            cbsa_name state_code      state county_code  county
## 1: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 2: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 3: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 4: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 5: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
## 6: San Francisco-Oakland-Hayward, CA          6 California           1 Alameda
##    site_latitude site_longitude
## 1:      37.68753      -121.7842
## 2:      37.68753      -121.7842
## 3:      37.68753      -121.7842
## 4:      37.68753      -121.7842
## 5:      37.68753      -121.7842
## 6:      37.68753      -121.7842

# Check footers
tail(pm2004)

##          date source  site_id poc daily_mean_pm2_5_concentration    units
## 1: 12/14/2004    AQS 61131003   1                             11 ug/m3 LC
## 2: 12/17/2004    AQS 61131003   1                             16 ug/m3 LC
## 3: 12/20/2004    AQS 61131003   1                             17 ug/m3 LC
## 4: 12/23/2004    AQS 61131003   1                              9 ug/m3 LC
## 5: 12/26/2004    AQS 61131003   1                             24 ug/m3 LC
## 6: 12/29/2004    AQS 61131003   1                              9 ug/m3 LC
##    daily_aqi_value            site_name daily_obs_count percent_complete
## 1:              46 Woodland-Gibson Road               1              100
## 2:              59 Woodland-Gibson Road               1              100
## 3:              61 Woodland-Gibson Road               1              100
## 4:              38 Woodland-Gibson Road               1              100
## 5:              76 Woodland-Gibson Road               1              100
## 6:              38 Woodland-Gibson Road               1              100
##    aqs_parameter_code       aqs_parameter_desc cbsa_code
## 1:              88101 PM2.5 - Local Conditions     40900
## 2:              88101 PM2.5 - Local Conditions     40900
## 3:              88101 PM2.5 - Local Conditions     40900
## 4:              88101 PM2.5 - Local Conditions     40900
## 5:              88101 PM2.5 - Local Conditions     40900
## 6:              88101 PM2.5 - Local Conditions     40900
##                                  cbsa_name state_code      state county_code
## 1: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 2: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 3: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 4: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 5: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 6: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
##    county site_latitude site_longitude
## 1:   Yolo      38.66121      -121.7327
## 2:   Yolo      38.66121      -121.7327
## 3:   Yolo      38.66121      -121.7327
## 4:   Yolo      38.66121      -121.7327
## 5:   Yolo      38.66121      -121.7327
## 6:   Yolo      38.66121      -121.7327

tail(pm2019)

##          date source  site_id poc daily_mean_pm2_5_concentration    units
## 1: 11/11/2019    AQS 61131003   1                           13.5 ug/m3 LC
## 2: 11/17/2019    AQS 61131003   1                           18.1 ug/m3 LC
## 3: 11/29/2019    AQS 61131003   1                           12.5 ug/m3 LC
## 4: 12/17/2019    AQS 61131003   1                           23.8 ug/m3 LC
## 5: 12/23/2019    AQS 61131003   1                            1.0 ug/m3 LC
## 6: 12/29/2019    AQS 61131003   1                            9.1 ug/m3 LC
##    daily_aqi_value            site_name daily_obs_count percent_complete
## 1:              54 Woodland-Gibson Road               1              100
## 2:              64 Woodland-Gibson Road               1              100
## 3:              52 Woodland-Gibson Road               1              100
## 4:              76 Woodland-Gibson Road               1              100
## 5:               4 Woodland-Gibson Road               1              100
## 6:              38 Woodland-Gibson Road               1              100
##    aqs_parameter_code       aqs_parameter_desc cbsa_code
## 1:              88101 PM2.5 - Local Conditions     40900
## 2:              88101 PM2.5 - Local Conditions     40900
## 3:              88101 PM2.5 - Local Conditions     40900
## 4:              88101 PM2.5 - Local Conditions     40900
## 5:              88101 PM2.5 - Local Conditions     40900
## 6:              88101 PM2.5 - Local Conditions     40900
##                                  cbsa_name state_code      state county_code
## 1: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 2: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 3: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 4: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 5: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
## 6: Sacramento--Roseville--Arden-Arcade, CA          6 California         113
##    county site_latitude site_longitude
## 1:   Yolo      38.66121      -121.7327
## 2:   Yolo      38.66121      -121.7327
## 3:   Yolo      38.66121      -121.7327
## 4:   Yolo      38.66121      -121.7327
## 5:   Yolo      38.66121      -121.7327
## 6:   Yolo      38.66121      -121.7327

# Check variable names
paste(colnames(pm2004))

##  [1] "date"                           "source"                        
##  [3] "site_id"                        "poc"                           
##  [5] "daily_mean_pm2_5_concentration" "units"                         
##  [7] "daily_aqi_value"                "site_name"                     
##  [9] "daily_obs_count"                "percent_complete"              
## [11] "aqs_parameter_code"             "aqs_parameter_desc"            
## [13] "cbsa_code"                      "cbsa_name"                     
## [15] "state_code"                     "state"                         
## [17] "county_code"                    "county"                        
## [19] "site_latitude"                  "site_longitude"

# Check variable types
sapply(pm2004, typeof)

##                           date                         source 
##                    "character"                    "character" 
##                        site_id                            poc 
##                      "integer"                      "integer" 
## daily_mean_pm2_5_concentration                          units 
##                       "double"                    "character" 
##                daily_aqi_value                      site_name 
##                      "integer"                    "character" 
##                daily_obs_count               percent_complete 
##                      "integer"                       "double" 
##             aqs_parameter_code             aqs_parameter_desc 
##                      "integer"                    "character" 
##                      cbsa_code                      cbsa_name 
##                      "integer"                    "character" 
##                     state_code                          state 
##                      "integer"                    "character" 
##                    county_code                         county 
##                      "integer"                    "character" 
##                  site_latitude                 site_longitude 
##                       "double"                       "double"

# Check for issues in key variables:
str(pm2004) # General readout

## Classes 'data.table' and 'data.frame':   19233 obs. of  20 variables:
##  $ date                          : chr  "01/01/2004" "01/02/2004" "01/03/2004" "01/04/2004" ...
##  $ source                        : chr  "AQS" "AQS" "AQS" "AQS" ...
##  $ site_id                       : int  60010007 60010007 60010007 60010007 60010007 60010007 60010007 60010007 60010007 60010007 ...
##  $ poc                           : int  1 1 1 1 1 1 1 1 1 1 ...
##  $ daily_mean_pm2_5_concentration: num  11 12.2 16.5 19.5 11.5 32.5 15.5 29.9 21 16.9 ...
##  $ units                         : chr  "ug/m3 LC" "ug/m3 LC" "ug/m3 LC" "ug/m3 LC" ...
##  $ daily_aqi_value               : int  46 51 60 67 48 94 58 88 70 61 ...
##  $ site_name                     : chr  "Livermore" "Livermore" "Livermore" "Livermore" ...
##  $ daily_obs_count               : int  1 1 1 1 1 1 1 1 1 1 ...
##  $ percent_complete              : num  100 100 100 100 100 100 100 100 100 100 ...
##  $ aqs_parameter_code            : int  88502 88502 88502 88502 88502 88502 88502 88502 88502 88502 ...
##  $ aqs_parameter_desc            : chr  "Acceptable PM2.5 AQI & Speciation Mass" "Acceptable PM2.5 AQI & Speciation Mass" "Acceptable PM2.5 AQI & Speciation Mass" "Acceptable PM2.5 AQI & Speciation Mass" ...
##  $ cbsa_code                     : int  41860 41860 41860 41860 41860 41860 41860 41860 41860 41860 ...
##  $ cbsa_name                     : chr  "San Francisco-Oakland-Hayward, CA" "San Francisco-Oakland-Hayward, CA" "San Francisco-Oakland-Hayward, CA" "San Francisco-Oakland-Hayward, CA" ...
##  $ state_code                    : int  6 6 6 6 6 6 6 6 6 6 ...
##  $ state                         : chr  "California" "California" "California" "California" ...
##  $ county_code                   : int  1 1 1 1 1 1 1 1 1 1 ...
##  $ county                        : chr  "Alameda" "Alameda" "Alameda" "Alameda" ...
##  $ site_latitude                 : num  37.7 37.7 37.7 37.7 37.7 ...
##  $ site_longitude                : num  -122 -122 -122 -122 -122 ...
##  - attr(*, ".internal.selfref")=<externalptr>

summary(pm2004) #Summary statistics

##      date              source             site_id              poc        
##  Length:19233       Length:19233       Min.   :60010007   Min.   : 1.000  
##  Class :character   Class :character   1st Qu.:60370002   1st Qu.: 1.000  
##  Mode  :character   Mode  :character   Median :60658001   Median : 1.000  
##                                        Mean   :60588026   Mean   : 1.816  
##                                        3rd Qu.:60750006   3rd Qu.: 2.000  
##                                        Max.   :61131003   Max.   :12.000  
##                                                                           
##  daily_mean_pm2_5_concentration    units           daily_aqi_value 
##  Min.   : -0.10                 Length:19233       Min.   :  0.00  
##  1st Qu.:  6.00                 Class :character   1st Qu.: 25.00  
##  Median : 10.10                 Mode  :character   Median : 42.00  
##  Mean   : 13.13                                    Mean   : 46.33  
##  3rd Qu.: 16.30                                    3rd Qu.: 60.00  
##  Max.   :251.00                                    Max.   :301.00  
##                                                                    
##   site_name         daily_obs_count percent_complete aqs_parameter_code
##  Length:19233       Min.   :1       Min.   :100      Min.   :88101     
##  Class :character   1st Qu.:1       1st Qu.:100      1st Qu.:88101     
##  Mode  :character   Median :1       Median :100      Median :88101     
##                     Mean   :1       Mean   :100      Mean   :88267     
##                     3rd Qu.:1       3rd Qu.:100      3rd Qu.:88502     
##                     Max.   :1       Max.   :100      Max.   :88502     
##                                                                        
##  aqs_parameter_desc   cbsa_code      cbsa_name           state_code
##  Length:19233       Min.   :12540   Length:19233       Min.   :6   
##  Class :character   1st Qu.:31080   Class :character   1st Qu.:6   
##  Mode  :character   Median :40140   Mode  :character   Median :6   
##                     Mean   :35328                      Mean   :6   
##                     3rd Qu.:41860                      3rd Qu.:6   
##                     Max.   :49700                      Max.   :6   
##                     NA's   :1253                                   
##     state            county_code        county          site_latitude  
##  Length:19233       Min.   :  1.00   Length:19233       Min.   :32.63  
##  Class :character   1st Qu.: 37.00   Class :character   1st Qu.:34.07  
##  Mode  :character   Median : 65.00   Mode  :character   Median :36.48  
##                     Mean   : 58.63                      Mean   :36.23  
##                     3rd Qu.: 75.00                      3rd Qu.:38.10  
##                     Max.   :113.00                      Max.   :41.71  
##                                                                        
##  site_longitude  
##  Min.   :-124.2  
##  1st Qu.:-121.6  
##  Median :-119.3  
##  Mean   :-119.7  
##  3rd Qu.:-117.9  
##  Max.   :-115.5  
## 

summary(pm2004$daily_mean_pm2_5_concentration) #Key variable

##    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
##   -0.10    6.00   10.10   13.13   16.30  251.00

mean(is.na(pm2004$daily_mean_pm2_5_concentration)) #No missing values

## [1] 0

hist(pm2004$daily_mean_pm2_5_concentration, breaks = 100, xlim=c(0,100)) #Check for outliers

str(pm2019) # General readout

## Classes 'data.table' and 'data.frame':   53086 obs. of  20 variables:
##  $ date                          : chr  "01/01/2019" "01/02/2019" "01/03/2019" "01/04/2019" ...
##  $ source                        : chr  "AQS" "AQS" "AQS" "AQS" ...
##  $ site_id                       : int  60010007 60010007 60010007 60010007 60010007 60010007 60010007 60010007 60010007 60010007 ...
##  $ poc                           : int  3 3 3 3 3 3 3 3 3 3 ...
##  $ daily_mean_pm2_5_concentration: num  5.7 11.9 20.1 28.8 11.2 2.7 2.8 7 3.1 7.1 ...
##  $ units                         : chr  "ug/m3 LC" "ug/m3 LC" "ug/m3 LC" "ug/m3 LC" ...
##  $ daily_aqi_value               : int  24 50 68 86 47 11 12 29 13 30 ...
##  $ site_name                     : chr  "Livermore" "Livermore" "Livermore" "Livermore" ...
##  $ daily_obs_count               : int  1 1 1 1 1 1 1 1 1 1 ...
##  $ percent_complete              : num  100 100 100 100 100 100 100 100 100 100 ...
##  $ aqs_parameter_code            : int  88101 88101 88101 88101 88101 88101 88101 88101 88101 88101 ...
##  $ aqs_parameter_desc            : chr  "PM2.5 - Local Conditions" "PM2.5 - Local Conditions" "PM2.5 - Local Conditions" "PM2.5 - Local Conditions" ...
##  $ cbsa_code                     : int  41860 41860 41860 41860 41860 41860 41860 41860 41860 41860 ...
##  $ cbsa_name                     : chr  "San Francisco-Oakland-Hayward, CA" "San Francisco-Oakland-Hayward, CA" "San Francisco-Oakland-Hayward, CA" "San Francisco-Oakland-Hayward, CA" ...
##  $ state_code                    : int  6 6 6 6 6 6 6 6 6 6 ...
##  $ state                         : chr  "California" "California" "California" "California" ...
##  $ county_code                   : int  1 1 1 1 1 1 1 1 1 1 ...
##  $ county                        : chr  "Alameda" "Alameda" "Alameda" "Alameda" ...
##  $ site_latitude                 : num  37.7 37.7 37.7 37.7 37.7 ...
##  $ site_longitude                : num  -122 -122 -122 -122 -122 ...
##  - attr(*, ".internal.selfref")=<externalptr>

summary(pm2019) #Summary statistics

##      date              source             site_id              poc        
##  Length:53086       Length:53086       Min.   :60010007   Min.   : 1.000  
##  Class :character   Class :character   1st Qu.:60310004   1st Qu.: 1.000  
##  Mode  :character   Mode  :character   Median :60612003   Median : 3.000  
##                                        Mean   :60565291   Mean   : 2.562  
##                                        3rd Qu.:60771002   3rd Qu.: 3.000  
##                                        Max.   :61131003   Max.   :21.000  
##                                                                           
##  daily_mean_pm2_5_concentration    units           daily_aqi_value 
##  Min.   : -2.200                Length:53086       Min.   :  0.00  
##  1st Qu.:  4.000                Class :character   1st Qu.: 17.00  
##  Median :  6.500                Mode  :character   Median : 27.00  
##  Mean   :  7.734                                   Mean   : 30.56  
##  3rd Qu.:  9.900                                   3rd Qu.: 41.00  
##  Max.   :120.900                                   Max.   :185.00  
##                                                                    
##   site_name         daily_obs_count percent_complete aqs_parameter_code
##  Length:53086       Min.   :1       Min.   :100      Min.   :88101     
##  Class :character   1st Qu.:1       1st Qu.:100      1st Qu.:88101     
##  Mode  :character   Median :1       Median :100      Median :88101     
##                     Mean   :1       Mean   :100      Mean   :88214     
##                     3rd Qu.:1       3rd Qu.:100      3rd Qu.:88502     
##                     Max.   :1       Max.   :100      Max.   :88502     
##                                                                        
##  aqs_parameter_desc   cbsa_code      cbsa_name           state_code
##  Length:53086       Min.   :12540   Length:53086       Min.   :6   
##  Class :character   1st Qu.:31080   Class :character   1st Qu.:6   
##  Mode  :character   Median :40140   Mode  :character   Median :6   
##                     Mean   :35841                      Mean   :6   
##                     3rd Qu.:41860                      3rd Qu.:6   
##                     Max.   :49700                      Max.   :6   
##                     NA's   :4181                                   
##     state            county_code        county          site_latitude  
##  Length:53086       Min.   :  1.00   Length:53086       Min.   :32.58  
##  Class :character   1st Qu.: 31.00   Class :character   1st Qu.:34.14  
##  Mode  :character   Median : 61.00   Mode  :character   Median :36.63  
##                     Mean   : 56.39                      Mean   :36.35  
##                     3rd Qu.: 77.00                      3rd Qu.:37.97  
##                     Max.   :113.00                      Max.   :41.76  
##                                                                        
##  site_longitude  
##  Min.   :-124.2  
##  1st Qu.:-121.6  
##  Median :-119.8  
##  Mean   :-119.8  
##  3rd Qu.:-118.1  
##  Max.   :-115.5  
## 

summary(pm2019$daily_mean_pm2_5_concentration) #Key variable

##    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
##  -2.200   4.000   6.500   7.734   9.900 120.900

mean(is.na(pm2019$daily_mean_pm2_5_concentration)) #No missing values

## [1] 0

hist(pm2019$daily_mean_pm2_5_concentration, breaks = 100, xlim=c(0,100)) #Check for outliers

Summary of findings: While the Max values of PM 2.5 in each of these data sets is extremely high, they don’t seem to be errors - just extreme events.

Problem 2. Combine the two years of data into one data frame. Use the Date variable to create a new column for year, which will serve as an identifier. Change the names of the key variables so that they are easier to refer to in your code.

# Combine the two years of data into one data frame.
pm <- rbind(pm2004, pm2019)

# Use the Date variable to create a new column for year, which will serve as an identifier.
dates <- pm$date
dates2 <- as.POSIXct(dates, format = "%m/%d/%Y")
dates3 <- format(dates2, format="%Y") 

pm <-  mutate(pm, year = dates3) #New column "year" added

# Change the names of the key variables so that they are easier to refer to in your code.
pm <- rename(pm, pm25 = daily_mean_pm2_5_concentration)

pm$year <- as.numeric(pm$year) #so that colorNumeric works, but can instead use colorFactor

Problem 3. Create a basic map in leaflet() that shows the locations of the sites (make sure to use different colors for each year). Summarize the spatial distribution of the monitoring sites.

# Create a basic map in leaflet() that shows the locations of the sites (make sure to use different colors for each year).
pal <- colorNumeric(palette = "RdYlBu", domain=c(2004, 2019)) 
#colorNumeric doesn't work any more

leaflet(pm) %>%
  addProviderTiles('OpenStreetMap') %>% 
  addCircles(lat=~site_latitude,lng=~site_longitude, color=pal(pm$year), opacity=1, fillOpacity=1, radius=100)

  #addLegend('bottomleft', pal=pal, values=~c(2004, 2019),
          #title='Site Locations', opacity=1)
    #this legend is driving me crazy

Summarize the spatial distribution of the monitoring sites: ???

Problem 4. Check for any missing or implausible values of PM2.5 in the combined dataset. Explore the proportions of each and provide a summary of any temporal patterns you see in these observations.

Problem 5. Explore the main question of interest at three different spatial levels. Create exploratory plots (e.g. boxplots, histograms, line plots) and summary statistics that best suit each level of data. Be sure to write up explanations of what you observe in these data.

State County Site in Los Angeles